This invention relates to orthopedic replacement surgery, and more particularly to a reference system for the implantation of condylar total knee prostheses, a tenser for stretching the knee ligaments when the knee joint is flexed for producing a force between the femur and the tibia during an operation using the aforementioned reference system, a drilling template for making bores in the tibia for attaching such a reference system, and a procedure for carrying out exact osteotomies on the tibia and on the femur for the implantation of condylar total knee prostheses.
The inventive reference system enables the surgeon to perform the osteotomies extremely precisely. This is a prerequisite for being able to carry out the implantation in such a way that the correct mechanical axis of the leg is produced by means of the operation.
It has been demonstrated that achievement of the correct mechanical axis of the leg is one of the most important prerequisites for long life of the knee prosthesis without loosening and pain; cf. Bargren, J. H., et al., "Alignment in Total Knee Arthroplasty," Clinical Orthopaedics and Related Research, No. 173 (1983), pp. 178-183.
In this connection, it is not only a matter of bringing about the correct static knee structure (alignment), but it is likewise important for balanced tension of the knee ligaments to be present, insofar as they still exist, or the correct soft-tissue tension.
Condylar knee prostheses consist of a component fixed to the femur and a component fixed to the tibia. Unlike the hinge prosthesis, these components are not connected by artificial mechanical aids.
As in the natural knee joint, the flexible connection between the two components is made up of ligaments and muscles insofar as they are preserved during implantation of the prosthesis. Before the prosthesis components can be attached to the femur and the tibia by means of clamping, wedging, or bone cement, the femur and tibia must be shaped to fit the prosthesis with the aid of bone saws and other tools. The instruments generally offered by the manufacturers of the knee prostheses serve primarily to carry out the required matching bone cuts on the femur and the tibia, the osteotomies, with the necessary accuracy.
An essential requirement in this connection is that the components of the knee prosthesis which slide against one another when the knee is bent and straightened must always occupy correct relative positions, i.e., the mechanical axis of the leg must not deviate from the physiological axis of the leg by more than 3.degree. varus or 3.degree. valgus, and that correct tension of the various ligaments must be achieved, which produces good stability of the knee joint during both extension and flexion.
As a rule, the prior art instrumentaria for the implantation of condylar total knee prostheses comprise the following means:
means for aligning the tibia with the femur for attaining the desired leg-axis position;
means for carrying out osteotomies, in the form of cutting gauges serving to guide the saw; such cutting gauges are conformed to specific shapes of prostheses and can usually be used for various sizes of one type of prosthesis;
means for producing the desired tension of the knee ligaments.
Such instrumentaria are described, for example, in the following publications: "Immediate Interlock Without Cement--The TRICON-P.TM. Cementless Tibial Component with FLEX-LOX.TM. pegs," Memphis, Tenn., Richards Medical Company, 4/1983; Pappas, Michael J., et al., "N.J. Knee Instrumentation System: Biomechanical and Surgical Rationale," Bio-Medical Engineering Corp. Technical Report, 3,1983; "Surgical Technique Using AOR.TM. Total Knee Instrumentation for the Miller/Galante Porous Tivanium Total Knee System," Warsaw, Ind., Zimmer, undated (received 11/1986), pp. 8 & 18-20; "The Intermedics Natural-Knee.TM. System: Instrumentation," Austin, Tex., Intermedics Orthopedics, 2/1986; "Precise Bone Cuts . . . Every Time--The Howmedical.RTM. Universal Total Knee Instrument System," Rutherford, N.J., Howmedica, Inc., 1980 (1/1982), pp. 22-25 and unnumbered page.
The prior art instrumentaria have the drawback that the cutting gauge for the osteotomies has two reference systems, viz., one on the tibia for cutting thereon, and a second one on the femur for cutting on that bone. For determining the cutting planes and for carrying out the osteotomy with the saw on the tibia, measuring means and cutting gauge are first attached to the tibia, e.g., by means of Steinmann's nails or bone-screws. After the tibia cut has been effected, the measuring means and cutting gauge are attached to the femur. During this changeover, an exact geometric relationship between the tibia-side and femur side components of the prosthesis is not ensured. Almost any surgeon who implants condylar total knee prostheses does, in fact, know of errors in this regard. Such errors are described, for instance, in Lotke, P. A. et al., "Influence of Positioning of Prosthesis in Total Knee Replacement," J. of Bone and Joint Surgery, No. 55-A (1977), pp. 77-79.
Steps have already been taken to avoid the aforementioned drawback, e.g., by fastening the knee to the operating table with a mechanical device, the saw also being connected to this device (cf. Cooke, T. D. V. et al., "Application of Bench-Mounted Saws for Precision Arthroplasty of the Arthritic Knee [Questor Knee Jigs]," Abstract Book, Second European Congress of Knee Surgery and Arthroscopy, Basel [Sept. 29-Oct. 4, 1986]; and J. Biomed. Eng., No. 7 [1985], pp. 45-50).
The devices described in the aforementioned publications comprise complicated mechanical structures which are time-consuming to use and also hamper access to the operating area.